It has been known to provide units to electrically monitor operational and environmental conditions of equipment located at operating sites. It has also been known to combine control units with monitoring units in order to control equipment when conditions out-of-range of programmed parameters are detected, and to allow a controller to correct the problem causing the out-of-range conditions. The equipment may be computers, data transmission equipment, sub-stations, processing equipment or other types of equipment, and may be unmanned, or may be manned by operators during the day but unmanned at night. Also, such sites even when operators are in attendance may have no maintenance personnel in attendance day or night.
One type of such monitor and control unit is a programmable controller disclosed in U.S. Pat. No. 4,748,654. As disclosed in this patent, the programmable controller is connected to sense equipment conditions and generate an alarm when conditions are sensed that deviate from a desired range of parameters, and then automatically dial one or a series of telephone numbers to locate maintenance or supervisory personnel through the use of the public telephone network. The controller is equipped to transmit over the telephone network to an operator at a dialed location, information about the alarm condition in the form of synthesized voice messages. The operator can use push-buttons on his telephone to produce dual tone, multi-frequency (DTMF) signals to enter various user access codes to receive information about the alarm conditions and to set switches and the like to control the equipment at the site.
In addition, through use of the push-button telephone, the operator can access the controller at the site through the use of a valid password to enter new parameters and can reprogram the controller at the site to correct conditions as they are recognized by the operator. For this purpose, the controller is programmable to define the source of control commands and the response to the control commands, depending on whether the apparatus is in an operator-controlled or automatic mode. In addition to the aforesaid U.S. Patent, further details of this type of programmable controller may be obtained by referring to application Ser. No. 07/149,671, filed Jan. 28, 1988, now U.S. Pat. No. 4,996,703. The disclosures of these applications and patents are incorporated by reference.